Sound amplifier



J. B. MITCHEL.

SOUND AMPLIFIER. APPLICATxoN FILED ocr. 15, 1919.

A 1,408,761. y Patented Mar. 7, 1922,

UNITED smilies PATENT QFFICE.

JOHN BERNARD MTCHEL. 0F BGVJYANVILLE, ONTARIO, CANADA.

.Application filed October' 15, 1919.

novel features of construction whereby thev sound is conducted from the tone arm through a substantially bell shaped sound chamber constructed of brass or like material and preferably having a vibratory top of like material and is emitted through a chamber having sound deflecting boards therein.

'The objects of the invention are to provide a form of sound amplifier' capable of reproducing the full volume of `the sound received from the tone arm and at the saine time eliminating the metallic tone so conimon in phonographs and rendering the tone 'flexible and pure and generally to provide a sound amplifier which will be inexpensive to construct, durable and efficient.

In the drawings, Figure l is a plan view of the device with the top board of the cabinet removed.

Figure 2 is a sectional view taken on the line B-B of Figure l.

Figure 3 is a transverse sectional view taken on the line A-A of Figure 1.

Figure 4 is a plan view of a portion of the device showing a modified form of top for the amplifying chamber.

Like numerals of reference indicate cor responding parts in the various figures.

Referring to the drawings l is a chamber corresponding to the sound chamber usually employed in phonographs.

2 is a sound tube registering with an opening 3 in the top l on which the tone arm is mounted and extending downwardly in a forward curve to the base 5 on which it is supported, the opening through said tube being gradually enlarged from its top end and curving sufficiently that the delivery Specification of Letters Patent.

Patented Mar. '7, 1922.

serial No, accese.

end is substantially at right angles to the top or receiving end.

6 is a wooden casing of substantially bell shape in longitudinal section and secured to the base 5 with its smaller end registering with the delivery end of the tube 2 and receiving the sound therefrom, the bottom wall of said chamber 6 being supported on a horizontal plane by said base 5 while the top and side walls flare outwardly in bell shape.

The top of the chamber 6 is provided with a substantially bell shaped openingl into which is loosely fitted a correspondingly shaped cover .7 of brass secured at its reduced end to the end of the tube 2 while the flaring portion 8 thereof is unsupported and is free to vibrate upon the impact of the sound waves from the tone arm.

9 are brass plates with which the wooden walls of the sound chamber are lined.

l0 are springs adjustably held to engagement with the vibratory top 7 by means of screws ll passing therethrough into the reduced portion of said top, said springs forming a means for regulating the limit of vibration of said top, and preferably having their outer ends curved as at l2.

lil is a wooden casing substantially similar in shape to the casing 6 but being of greater dimensions, said casing 13 being so arranged within the chamber l that the reduced or rear side thereof engages the enlarged end of the casing G while the enlarged front portion terminates substantially flush with the front wall of said chamber l and completely lills the opening' therein.

lf desired the tube Q, and the casings (i and 13 may be constructed in one piece and provided with a metal lining and a central opening in the top to conform to the opening in the top of the chamber 6.

le are plates vertically arranged within the casing 13 and extending from front to rear thereof, said plates being tapered gradually rearwardly and presenting comparatively thin edges l5 at the mouth of the casing 6.

In the operation of this invention the sound waves flow downwardly from the tone arm through the wooden tube 2 and are directed to the casing 6 in which they are permitted to expand and engage the brass walls of the casing and the vibratory top 7 which tends to eliminate the raspy nasal sound so common in talking machines. Should it be found that the springs 10 exert too great pressure on the top T they may of course be loosened or may if necessary be dispensed with altogether.

Thile itis preferable that the top of the casing 6 be permitted to vibrate correspondingly to the tone Waves, said top may also he constructed of a solid piece of brass or like material with very satisfactory results.

In Figure 1 a modified form of amplifier is shown in which the top thereof is completely covered by a metal 'plate 16 secured to the reduced end thereof.V

As the sound flows from the chamber 6 into the larger chamber 13 the expansion thereof is greatly facilitated by means of the tapered plates 14 which deeet it to all parts of said chamber.

lVhile I havethus described the preferred construction, combination and arrangement of parts Which constitute the present invention, it is obvious that others skilled in the arts of which this appertains, may make various changes Without departing from the spiritaud scope of the invention as contained in the claims for novelty following.

that I claim is:

1. In a sound amplifier, in combination, an amplifying chamber, a plate forming an intermediate section of the top Wall of said amplifying chamber, said plate being mounted at its innermost end, and springr means controlling' the freedom of vibration of said plate.

2. In a sound amplifier, in combination, an intermediate amplifying chamber having a metal lining, a metal plate mounted at its inner end and constituting ar section of the top wall of said chamber, and a spring finger secured to the mounted end of said plate and projecting over the free portion thereof.

3. In aY sound amplifier, in combination` a tone arm, a sound conducting tube from said tone arm, a delivery chamber, an intermediate amplifying chamber receiving the sound from said tube and delivering same to said delivery chamber, said intermediate chamber being substantially bell shape in longitudinal section and havingl its smaller end engaging said sound tube and its enlarged end engaging with an opening corresponding in size to the smaller end of said delivery chamber, a vibratory plate closing in the top of said intermediate chamber and springs adjustably mounted to permit of regulating the vibration of said vibrator)Y plate.

Signed at the city of Toronto, 4this 27th day of September 1919.

JOHN BERNARD MITCH ICL.

lVitnesses z W. G. HAMMOND, C. A. RICHARDSON. 

